thoughts about learning…and other matters

Leaving the answer blank

If you don’t know the answer, should you leave it blank or should you guess? An argument can be made on each side:

On the one hand, many tests (such as the SAT and the AMC) penalize random guesses by giving more credit for a blank answer than a wrong one. On a multiple-choice test this penalty can be enforced either by subtracting a fraction of a point for a wrong answer or by adding a fraction of a point for a blank. Depending on the size of the fraction, one can calculate when it’s worth guessing — typically when at least two of the choices can be reasonably eliminated. While this sort of scoring system is rare for open response questions, it’s not unheard of. For instance, a professor who wishes to remain anonymous writes this:

In large first year classes I normally give students 40% for a blank exam and will take marks away for nonsense. They need to learn not to waste the TA’s time.

On the other hand, we teachers regularly tell students that almost any answer is better than none. If you put something down, you might earn some part credit; if you put nothing down, you’ll earn nothing. The MCAS, for example, is scored that way; it’s always better to guess.

Seeing what a student is thinking is never a waste of my time. Of course we don’t want students to write nonsense. But we want them to be willing to take risks. If we take the attitude of the professor quoted above, we are implicitly endorsing the immortal words of Homer Simpson: “If something’s hard to do, then it’s not worth doing.”

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About me

I have just completed my 20th year as a math teacher at Weston High School (the only public high school in Weston, MA, though sometimes it seems more like a private school). This is my 43rd year as a teacher altogether. I also teach at Harvard’s Crimson Summer Academy each summer (this will be the 14th!), and for 21 years I taught at the Saturday Course in Milton, MA. Until recently I served on the board of the Dorchester Historical Society.

I read, cook, and build my model railroad when I can. For some reason I’m left with less free time than would be ideal, but somehow I also manage to devote time to my wife, Barbara, and to our excessive number of cats.